How Radio Waves Carry Information

Sending Information With Radio Waves

Process Diagram

Radio waves can be modified to carry information in many ways.  Three ways are shown and described below.

The “Audio-frequency waves” shown below might be the electrical signal produced by a microphone when you speak into it.  It would also be the electrical signal sent to the speaker to produce the voice you hear coming from the radio.

The “Carrier waves” shown below are the radio waves produced by the transmitter at the frequency you have your radio set to.

The transmitter modifies the carrier waves by combining it with the audio frequency waves to produce a new radio wave.

One way to do this is by changing the carrier frequency.  This is known as frequency modulation (FM).  A picture of the resulting wave is shown below.

Another way of modifying the carrier wave’s amplitude (i.e., height).  This is known as amplitude modulation (AM).  A picture of the resulting wave is shown below.

These modified waves thus carry the audio frequency signal as they are transmitted from antenna to antenna through the air.  When this modulated signal gets to the receiver, the receiver pulls out the carrier wave and is left with the original audio frequency wave which it can send to the speaker.

Another way a radio wave can carry information is to just turn it on and off.  This is the way Morse code is sent.  Pictures of the carrier wave and the signal you get when you turn it on and off to send the letter C is shown below.

 

Ionosphere-High Frequency Radio Wave Reflection

Schematic diagram showing the propagation of high-frequency (shortwave) radio waves by reflection off the ionosphere

Specific ionization conditions vary greatly between day (left) and night (right), causing radio waves to reflect off different layers of the ionosphere or transmit through them, depending upon their frequency and their angle of transmission. Under certain conditions of location, ionization, frequency, and angle, multiple “skips,” or reflections between ionosphere and Earth, are possible. At night, with no intervening layers of the ionosphere present, reflection off the F layer can yield extremely long transmission ranges.

High-frequency (HF) radio is in the 100- to 10-metre wavelength band, extending from 3 megahertz to 30 megahertz. Much of the HF band is allocated to mobile and fixed voice communication services requiring transmission bandwidths of less than 12 kilohertz. International (shortwave radio) broadcasting also is conducted in the HF band; it is allocated to seven narrow bands between 5.9 megahertz and 26.1 megahertz.

THE RST SYSTEM

Readability

1–Unreadable
2–Barely readable, occasional words distinguishable.
3–Readable with considerable difficulty.
4–Readable with practically no difficulty.
5–Perfectly readable.

Strength (Signal strength can be read from the S meter when receiving.)

1–Faint signals, barely perceptible.
2–Very weak signals.
3–Weak signals.
4–Fair signals.
5–Fairly good signals.
6–Good signals.
7–Moderately strong signals.
8–Strong signals.
9–Extremely strong signals.

Tone

1–Sixty cycle ac or less, very rough and broad.
2–Very rough ac, very harsh and broad.
3–Rough ac tone, rectified but not filtered.
4–Rough note, some trace of filtering.
5–Filtered rectified ac but strongly ripple-modulated.
6–Filtered tone, definite trace of ripple modulation.
7–Near pure tone, trace of ripple modulation.
8–Near perfect tone, slight trace of modulation.
9–Perfect tone, no trace of ripple or modulation of any kind.

Signal reports are exchanged when Amateur Radio operators contact each other.
For Morse code (CW) communications, all three are used. A very good signal report would be 599.
For voice communications, only readability and strength are used. A very good signal report would be 59.

RADIO WAVE PROPAGATION

Introduction

Propagation means how radio waves get from the transmitter to the receiver.

High frequency radio waves can bounce off the ionosphere (i.e., a layer of the atmosphere high above the earth) and return to earth a long distance from the transmitter.  Starting at about 50 MHz (i.e., very high frequency or VHF) and higher, radio waves do not return to earth and are thus limited to being received within sight of the transmitter.  Examples are shown below:

HF Radio Waves Bounce Back to Earth and Make Long Distance Contacts Possible.

VHF and UHF Waves are Limited to Line of Sight. Distance Covered Can Be Increased by Using Repeater .

There are more Amateur Radio repeaters in Klang Valley.  One repeater can be linked together so communication around the state is possible with a HT.  Another repeaters are always linked so communications on one repeater are heard throughout the state.

Duplexer Fund

Dear Friends of MARES,

MARES is in the midst of collecting some fund for purchasing a duplexer, cost about RM6000.

The fund is handled by 9M2RS and 9M2ZC, with the assistant of 9W2ARN. At present we have collected about RM1450, and would need about RM4550 more to go. Current contributor includes 9M2RS, 9W2CCW, 9W2SLC and SCS friends, and 9W2TPT and various contributor at club house donation boxes.

We would like to appeal to all members, to support this fund, and would welcome generous donation from the members.

To donate, you can pass the donation via the following method:

1. At club house – Pass to the donation box

2. Via ATM, CDM, MBB2U -
    Name  : Abd. Rashid Sultan
    Maybank Account : 0142 5310 1180

Note for method 2: Kindly email the confirmation to 9M2ZC at klzbd@yahoo.com for compilation.

Upon reaching the RM6000 amount, the duplexer purchase will be handled by 9M2RS. Expected delivery for the purchase is about 1 weeks, upon order confirmation.

For more details, read the following Mailing list thread – http://groups.yahoo.com/group/mymares/message/3632

We would like to thank you for your kind contribution and would hope this would be a success.

Thank you.

***Info from MARES Site.